Electrophotographic image forming methods used for dry image forming apparatuses such as laser printers, copiers and facsimiles typically include the following processes:    (1) charging a surface of an image bearing member such as a photoreceptor (charging process);    (2) irradiating the charged surface of the image bearing member with light so that the charges of the irradiated portions decay, thereby forming an electrostatic latent image on the surface of the image bearing member (irradiating process);    (3) developing the electrostatic latent image with a developer including a charged dry toner to form a visible toner image on the image bearing member (developing process);    (4) transferring the toner image to a recording material such as a paper sheet (transferring process);    (5) fixing the toner image to the recording material upon application of heat and/or pressure (fixing process); and    (6) cleaning the surface of the image bearing member so that the image bearing member is ready for the next image forming operation.
Recently, there is an increasing need for an image forming apparatus capable of performing high speed image formation while saving fixing energy. Therefore, there is a need for toner capable of melting at a relatively low temperature.
Further, recent image forming apparatuses are required to produce high quality images. Therefore, for example, when a pictorial image is formed, a technique in that high glossiness is imparted to the surface of a recording material is used to produce a clear glossy image.
In order to impart high glossiness to the surface of a recording material, a technique in that a transparent toner is applied to a non-image area of a recording material bearing a color image thereon to decrease the difference in glossiness between the color image area and the non-image area; a technique in that a transparent toner is applied to the entire surface of a recording material; and the like techniques have been proposed.
In addition, a technique in that a color toner image and a transparent toner image are formed on a recording material, and the images are heated by a fixing device, followed by cooling and peeling the images from the fixing device to prepare a glossy image is proposed. Using these techniques make it possible to produce copies having little difference in glossiness between an image area and a non-image area.
By contrast, in the printing field, treatments such as UV varnish printing, varnishing, and polypropylene film laminating are performed to control the glossiness of a desired portion of a printed image on a recording material. For example, a technique in that after performing a usual printing operation, an additional spot printing operation is performed on a desired portion of the print using an additionally prepared plate and an UV varnish or the like to impart high glossiness to the portion is used. By using this technique, a print in which the portion subjected to the spot printing operation has as high glossiness as photographs and other portions thereof have relatively low glossiness can be produced. Namely, the print has large glossiness difference, and therefore the print can be differentiated from normal prints.
However, when such a print is produced using an offset printing method, it is necessary to prepare an additional plate for forming such a glossy portion. In addition, this method cannot be used for producing a small number of prints (e.g., prints which are similar but a part of which is different from each other) due to increase of running costs, i.e., the method can be used only for producing a large number of prints.
Since electrophotography can perform image formation without using a plate, it becomes possible to produce such prints even when the number of the prints is small.
In attempting to produce images having different glossiness using electrophotography, a method in which a color toner image is formed on a recording material using at least one color toner (such as yellow, magenta or cyan toner) and a transparent toner, wherein an image portion having the transparent toner image has glossiness different from the glossiness of the color image portion by ±20% or more due to difference of the melting points of the color toner and the transparent toner; a method in which after a fixed color toner image is formed, an image is formed using a transparent toner while decreasing the fixing temperature to prepare an image portion having high glossiness and another image portion having relatively low glossiness; and a method in which initially a fixed glossy image is formed and a non-glossy image is then formed and fixed, have been proposed. By using these methods, a copy having portions with different glossiness can be produced, but the glossiness of a glossy image portion of the copy is lower than the glossy portion of a pictorial print formed by the above-mentioned spot printing method.
Since a low temperature fixable toner has such a property as to be easily melted, the low temperature fixable toner is preferably used as a transparent toner because a glossy image can be formed with low fixing energy. However, when a low temperature fixable toner is prepared merely by decreasing the melting point of the toner, the toner tends to cause a preservation problem in that the toner has a poor preservability (for example, the toner is agglomerated when preserved at a high temperature). In addition, such toner tends to cause a hot offset problem in that a part of a toner image on a recording material adheres to the surface of a fixing member of a fixing device when the toner image is fixed at a relatively high temperature, and the transferred image is then transferred onto another portion of the recording material bearing the toner image or another recording material, thereby deteriorating the image qualities of the toner images.
For these reasons, the inventors recognized that there is a need for an image forming method which produces glossy images like photographic images at a low fixing temperature without causing the offset problem and the preservation problem.